1. Field of the Invention
The present invention relates to a light amount adjusting apparatus and an optical apparatus. More specifically, the present invention relates to a light amount adjusting device in optical apparatus in which a lens is exchangeable or optical apparatus formed integrally with a lens.
2. Description of the Related Art
Conventionally, light amount adjusting devices used for imaging apparatuses such as video cameras, digital cameras, and the like have a structure in which two light amount adjusting blades are movably sandwiched between a base plate provided with an opening on the optical axis thereof and a cover. The two light amount adjusting blades can linear-slidably move in relatively-opposite directions in a planer perpendicular to the optical axis and can flexibly change the shape of the opening so as to adjust light amount. In the conventional light amount adjusting apparatuses, the configuration number of light amount adjusting blades is two, and thus, the shape of the aperture opening in the narrowly limited state is substantially diamond. In this case, the shape of blur/the shape of surface reflection ghost generated from a point light source looks like a diamond, which leads to a reduction in quality and is not suitable for high-grade and highly accurate imaging apparatuses. However, since the conventional light amount adjusting apparatuses have high space efficiency and are inexpensive, the conventional light amount adjusting apparatuses are often mounted to imaging apparatuses for general consumers.
In addition to the aforementioned light amount adjusting apparatus constituted by two light amount adjusting blades, there is another light amount adjusting apparatus having a structure, so-called, an iris diaphragm in which three or greater number of light amount adjusting blades are movably sandwiched between a base member provided with an opening on the optical axis thereof and a cover. The iris diaphragm is driven by a driving source via an engaging member, with which a plurality of light amount adjusting springs engages, extending from a blade driving ring which is pivoted about the optical axis. Here, examples of the driving source include a galvanometer, a stepping motor, and the like. The three or greater number of light amount adjusting blades are arranged one on top of the other on the blade driving ring in the clockwise direction or in the anticlockwise direction. The hole of one light amount adjusting blade is rotatably joined to a rotary shaft pin provided on the base member, and a drive pin provided on the blade driving ring is joined to an elongated hole section of the light amount adjusting blade. Furthermore, other light amount adjusting blades are also supported by the same structure. When the blade driving ring is rotated about, the optical axis, the plurality of light amount adjusting blades is also swung into interlock engagement with the blade driving ring, so that the light amount passing through the opening can be adjusted by changing the shape of the opening.
In the iris diaphragm device, the shape of the opening is determined by a plurality of light amount adjusting blades. Thus, the shape of the aperture opening in the narrowly limited state is a polygon and the shape of blur/the shape of surface reflection ghost generated from a point light source is close to a circle, so that the iris diaphragm device is mounted to high-grade and highly accurate imaging apparatuses. When the operating angle of the drive ring can be in a wide range, the amount of movement of each blade with respect to the rotation angle of the drive ring becomes small, high resolution control can be achieved until the aperture opening becomes small, exhibiting high sensitivity. In recent years, high-grade and highly accurate imaging apparatuses have become increasingly popular as imaging apparatuses for general consumers. In order to achieve an improvement in quality of the shape of blur/the shape of surface reflection ghost generated from a point light source, it is preferable that a light amount adjusting apparatus is constituted by a plurality of light amount adjusting blades as many as possible so as to bring the polygonal shape of the opening closer to a circle.
For example, Japanese Patent Laid-Open No. 2003-121901 discloses a light amount adjusting apparatus with a speed reduction ratio increased by the intervention of a drive gear serving as a drive transmission member fixed to the rotary shaft of a driving source in order to achieve transmission of the driving of the driving source and an intermediate gear member provided between the drive gear and the blade driving ring. Also, Japanese Patent Laid-Open No. 2007-163827 discloses a light amount adjusting apparatus in which blade rotation reference pins are provided to a blade driving member.
In order to bring the shape of the iris diaphragm closer to a circle as described above, the number of blades needs to be increased. However, a pitch in the circumferential direction of the rotation reference pins for the blades narrows with an increase in the number of blades. With this arrangement, a space for the engaging part which engages with the driving source and extends from the blade driving ring cannot be ensured. Thus, the operating angle of the drive ring becomes small, resulting in a difficulty in ensuring desired resolution. When the speed reduction ratio of the drive ring increases with the avoidance of the rotation reference pins, the space for the coupling section needs to be enlarged in the radial direction. Japanese Patent Laid-Open No. 2003-121901 also discloses a light amount adjusting device with a speed reduction ratio increased by the intervention of a stepping motor serving as a driving source, a drive gear serving as a drive transmission member fixed to the rotary shaft of the driving source in order to achieve transmission of the driving of the driving source, and an intermediate gear member provided between the drive gear and the blade driving ring. With this arrangement, the space for the coupling section and the speed reduction ratio of the drive ring can be increased. However, since the number of gear components is increased by one, the problems of backlash, rattling, or the like may occur, resulting in an adverse effect on the accuracy of the imaging apparatus.
As disclosed in Japanese Patent Laid-Open No. 2007-163827, the rotation reference pins for the light amount adjusting blades are provided on the drive ring side. With this arrangement, the rotation angle of the blade driving ring can be increased regardless of the pitch between the blade rotation reference pins. However, since the rotation reference pins for the light amount adjusting blades are formed on the blade driving ring serving as a moving body, the shape of the opening may be deformed or a shift in the center axis of the opening may occur, resulting in an adverse effect on the quality of the imaging apparatus.